The growing complexity of semiconductor device designs in advanced technology nodes, involves both a decrease in structural dimensions and higher complexity of the device design. The mainstream methods for dimensional characterization of such devices are based on optical metrology approaches, broadly termed Optical Critical Dimensions (OCD) metrology. The optical reflectivity of the sample depends on the dimensional characteristics of the measured structure, allowing inference of the measured structure dimensions from the measured signal through appropriate modeling and interpretation tools.
Hybrid Metrology (HM) technique is aimed at improving the accuracy, precision or other metrology performance of measurements by combining information from different toolsets to provide increased metrology performance for complex multi-stack structures of various types, including FinFET devices (i.e. Field Effect transistor in which the conducting channel is wrapped by a thin silicon “fin”, which forms the body of the device).
According to the known HM approach, the information measured by a secondary toolset (typically, critical dimensions Scanning Electron Microscopy (CD-SEM)) is used as input constraint on the modeling analysis of a primary toolset (typically, optical critical dimension (OCD)).
For example, WO 2011/158239, assigned to the assignee of the present application, describes a system and method for use in metrology of patterned structures, including data input utility for receiving first type of data indicative of image data on at least a part of the patterned structure, and data processing and analyzing utility configured and operable for analyzing the image data, and determining a geometrical model for at least one feature of a pattern in the structure, and using this geometrical model for determining an optical model for second type of data indicative of optical measurements on a patterned structure. In this technique, optimization of the interpretation models of two tools (OCD and CD-SEM tools) is performed using measured data from both tools, by creating a combined model.
The information measured by the secondary toolset (CD-SEM) is typically used as input constraint on the modeling analysis of the primary toolset (OCD). This is a so-called “sequential hybridization” of data from one toolset to another. While this sequential hybridization is generally successful, there are cases where it does not sufficiently or at all improve the measurement results. This is because a “threshold” parameter used to analyze CD-SEM images does not provide a reading of the CD value at a well-defined height of the structure being measured, but the CD value provided corresponds to ill-defined heights, correlated with other parameters of the structure such, as side wall angle (SWA).
WO 15/125127, also assigned to the assignee of the present application, describes the technique enabling to remove the above-mentioned correlation for better matching of data (between at least two tools, and to a reference system) and thus provide better Hybrid Metrology results. This technique utilizes the concept of a so-called “co-optimization” based hybridization, where, for example, image analysis parameters of a secondary tool (e.g. CD-SEM, X-ray tool) are modulated by profile information from a primary tool, OCD (scatterometry), while the OCD extracted profile is concurrently optimized (to minimize errors) through addition of the results (CD) of e.g. CD-SEM.